This proposal has as its goal the study of therapeutic methods currently being used to assist premature infants in compensating for decreased FRC (HMD). They will be studied in terms of the best way to evaluate treatment and prevent complications of treatment. To aid in the interpretation of the effects of therapy certain aspects of the control of the circulation will be studied. Research will be directed on 4 particular areas. (A) Control of breathing. The responsiveness to CO2 and the effect of lung volume on response will be studied. Respiratory center output will be examined in apneic infants as well as in infants being removed from respirators. A classification of apnea will be developed and therapy evaluated. (B) Circulatory parameters. Blood pressure, peripheral blood and resistance will be determined in infants with hyaline membrane disease. Effect of various therapies on these parameters will be evaluated. An attempt will be made to determine criteria for a pre-shock phase in HMD. (C) The effects of assisted ventilation. Assisted ventilation techniques will be modified to prevent pulmonary oxygen toxicity. (D) To evaluate factors in the maternal environment (Caesarian section, prolonged rupture of membranes, ritodrine) which may influence maintenance of FRC.